Polyelectrolyte fluidized aqueous suspensions

ABSTRACT

1. A FLUIDIZED RESUSPENDABLE MINERAL SUSPENSION PULP CONTAINING SOLIDS LARGER THAN 65 MESH AND FINES SMALLER THAN 325 MESH AND SUBSTANTIALLY HOMOGENEOUS THROUGHOUT IN WHICH THE FINES ARE INTEGRATED WITH THE COARSE MATERIAL BY FROM 0.005 TO 5 POUNDS PER TON OF SOLIDS OF A WATER SOLUBLE POLYELECTROLYTE, WHICH IS AN AMPHOLYTIC LINEAR CARBON CHAIN VINYL POLYMER CONSISTING ESSENTIALLY OF RECURRING CARBAMYLETHYLENE AND CARBOXYETHYLENE LINKAGES AND NOT MORE THAN A MINOR AMOUNT OF NITRILOETHYLENE LINKAGES AND SALTS THEREOF, HAVING A WEIGHT AVERAGE MOLECULAR WEIGHT IN EXCESS OF 100,000, THEREBY PRODUCING A SUSPENSION WHICH IS OF UNIFORM CHARACTERISTICS, FROM WHICH THE SOLIDS DROP OUT AS AN UNCLASSIFIED RAIDALLY RESUSPENDABLE THIXTROPIC MATERIAL, SAID POLYMER INCREASING THE VISCOSITY OF THE AQUEOUS PHASE, INSURING LAMINAR FLOW AT HIGHER VELOCITIES, THEREBY REDUCING PUMPING POWER REQUIREMENTS, SO THAT DURING INTER TANEOUSLY STABILIZING THE SUSPENSION, SO THAT DURING INTERRUPTIONS IN AGITATION, THE SUSPENSION REMAINS FLUIDIZED, AND IN PUMPABLE CONDITION.

15 1974 R. B. BOOTH I "/0 OF TOTAL I50 MESH SILICA IN UPPER HALF OFSUSPENSION N I O O I POLYELECTROLYTE FLUIDIZED AQUEOUS SUSPENSIONSOriginal Filed July 27, 1970 FlG.l

' POLYAGRYLAM/DE GLUE I 1 1 I I l I l I I fi s |o 15 POLYACRYLAMIDE-THOUSANTHS OF POUNDS PER TON 0F souos TENTH$ 0F POUNDS PER TON 0F sounsFIG. 2

P LYAGRYLAM/DE m w 0. 0/ poqlvas/ 7'0/V OF TOTAL I50 MESH SILICA INUPPER HALF OF SUSPENSION GL UE 0.13 POUNDS/ TON "United States Patent3,842,013 POLYELECTROLYTE FLUIDIZED AQUEOUS SUSPENSIONS Robert BenBooth, Stamford, Conn., assignor to American Cyanamid Company, Stamford,Conn. Application July 27, 1970, Ser. No. 58,338, now Patent N 0.3,741,641, which is a continuation-in-part of application Ser. No.179,287, Mar. 7, 1962, now Patent No. 3,524,682, which in turn is acontinuation-in-part of application Ser. No. 698,429, Nov. 25, 1957.Divided and this application Nov. 17, 1972, Ser. No. 307,664 Int. Cl.B01j 13/00 U.S. Cl. 252-315 4 Claims ABSTRACT OF THE DISCLOSURE Aqueoussuspensions of solids with a wide particle size range havingcomparatively coarse materials including some larger than 65 mesh andvery fine materials including some smaller than 325 mesh settle out withthe solids in unclassified and in resuspendable form, when settling inthe hindered state under non-Stokes conditions, is effected in thepresence of a polymer of the acrylamideacrylic acid-acrylonitrile typewhich causes the fines to remain with the large particles and settle outcomparatively homogeneously.

This aids in preventing deposits of coarse materials in settling tanks,leach tanks, internal combustion engines and their radiators, heatexchangers, cooling towers, flowing streams in natural or man-made watercourses, and mine operations, and the polymer in solution can penetrateinto coarse material with fines so that settled material can beresuspended, even if the polymer is introduced after at least somesettling has occurred.

CROSS-REFERENCES This is a division, of application Ser. No. 58,338filed July 27, 1970, now Pat. No. 3,741,641 dated July 17, 1973, whichis a continuation-in-part of application Ser. No. 179,287, filed Mar. 7,1962, now Pat. No. 3,524,682, Aug. 18, 1970, Coal Suspension Pumping,which in turn is a continuation-in-part of application Ser. No. 698,429,[filed Nov. 25, 1957, entitled Flu-idizing Aqueous Suspensions ofSolids, now abandoned.

SUMMARY OF THE INVENTION This invention relates to the fiuidizing offinely-divided solids such as ore and mineral suspensions, particularlythose containing a broad range of particle sizes, during leaching,particularly acid leaching, and related operations, particularly theacid leaching of uranium ores, by the use of a water-solublepolyele-ctrolyte. The term ore refers to any solid mineral crude whichcan be profitably processed. This includes maintaining the fluidity ofsuspensions of sand, or silt, or dredged materials, and maintainingsolids in resuspendable form, as in automobile radiators, heatexchangers, settling tanks, thickeners or other process equipment whichcould be adversely affected by fine solid materials settling out andcaking to interfere with subsequent circulation or heat transfer. Attimes pre-existing deposits are loosened and resuspended along with thesolids maintained in fluidized state. Such deposits are particularlypredominant in sewage lines, including sanitary, storm and industriallines, and circulating water lines such as pipes to and from coolingtowers, heat exchangers, radiators and lines to ballast tanks, dredgetanks, and spoil areas, and the like. Watersoluble linear polyalkaneshaving polycarboxy substituents, and conveniently, but not necessarilypolycarbamyl and polynitrilo groups are effective in the fluidizing.Preferably about 90% or more of the substituents are carbamyl groups.Other groups may be present which do not interfere with the basicsuspending action described.

In such operations as uranium ore leaching, the ore is ground, suspendedin water with an acid, and agitated as a suspension for a sufficientlength of time to dissolve. the recoverable uranium, and then the solidsare separated from the acid solution containing the uranium. Theleaching is conducted in tanks, and the minerals aremairb tained insuspension by agitation. Portions of the suspended minerals tend to dropout by gravity, and clog up the agitators, pipes, pumps, and otherleaching equipment Frequently, an aqueous suspension, through accidentor design, must remain in a quiescent state for various per-iods oftime. When permitted to remain in a quiescent state, there is a markedtendency for the coarser particles to drop out more rapidly than thefiner particles with a result that there is a layer formed at the bottomof the particular vessel consisting mainly of the coarser particles, andabove that is a layer which may or may not tend to drop out, containingthe more finely divided materials. In other words, a form ofclassification occurs. In this classification there is also a tendencyfor the heavy coarser particles to solidify or pack or cake. Sometimesthis does no particular damage, as for example, if the materials aresuspended in a conical bottom tank in which air or liquid can beintroduced at the bottom and thus stir up and disturb the solidmaterials. Sometimes even such tanks become clogged. Frequently,however, it is found that the dropping out of the solid particles causesdifficulties. For example, in a leaching tank the solid particles maypack around an agitator with such firmness that it is necesary for thelarger solid particles to be removed with water or air jets or evenpick-s and shovels to permit the agitator to again start operating. Dueto power outages or other accidental causes, it is not unusual for atank to lose its agitation, and when power is again ready to be applied,it is found the agitators are so firmly frozen in position that theagitator motors burn out, or blow fuses or circuit breakers. Sometimesagitator blades or shafts are snapped.

In many instances this problem has been to some extent overcome 'byattempting to design equipment which minimizes the problem. As abovementioned, conical bottom tanks in which air streams can be introducedat the bottom are not so subject to clogging and, if clogged, cansometimes be placed back in operation by air action alone. In manyinstances it is admittedly desirable to be able to use flat bottom tanksor smaller pipes for treatment of the suspensions, but because of knowndifiiculties, the system had to be designed to meet current operatingstandards, even though such design practice may have markedly increasedthe cost of the plant.

To some extent efforts have been made to overcome this difiiculty byintroducing agents, such as glue, into the suspended solids. The use ofglue is sharply limited by the variation in its effect with pH and thecomparatively large quantities required, which raise the cost ofoperations. Under the highly acid conditions used for uranium oreleaching, glue largely loses its effectiveness as a fluidizing agent.Glue is less effective at a pH range below 4 than at a pH of about 6.Glue has the further disadvantage that at lower pulp densities it isrelatively ineffective. For example, in decreasing the pulp density inone Canadian uranium leaching operation from the normal 65% solids to50%, glue in economic amounts failed to show a fluidizing effect. Forsome purposes, polymers of acrylic acid have been used withwater-swelling clays and bentonites to make thixotropic drilling mudswhich suspend drillcuttings when circulation stops. Addition ofbentonites to suspensions of ores and minerals in acid leachingoperations has not shown the same effect as in drilling oil wells BRIEFDESCRIPTION OF PERTINENT ART There are many patents and publications onthe interaction of polyelectrolytes and finely divided solids. Arepresentative but not exhaustive group of such references, US. Patentsexcept where .stated, includes:

1,976,679, Fikentscher et al., Production of Dispersions, Oct. 9, 1934,discloses the use of materials such as sodium salt or polymerizedacrylic acid with or without wetting agents or soaps for the dispersionof inorganic or organic pigments as a viscous dispersion for treatingfabrics.

2,327,302, Dittmar, Soap Composition, Aug. 17, 1943, discloses the useof a precipitate-inhibiting amount of an alkali metal salt of ahalogen-substituted polyacrylic acid as a hard water softening agent orfor redissolving precipitates already formed and mentions use in dyeing,water softening or boiler feed water.

2,328,901, Grimm et al., Nitrogenous Condensation Product, Sept. 7,1943, discloses polymeric acrylic amide, and similar unsaturated acidamides when polymerized are used in precipitating soluble dyes fordyeing fabrics and coloring leather.

2,533,166, Jones, Process for Polynierizing Water-SolublePolyacrylamides and Poly-Alpa-Substituted Acrylamides, Dec. 5, 1950-,discloses a method of producing polyacrylamides having a high peptizingaction to prevent the sedimentation of finely divided materials such aspigments and silver halide dispersed in aqueous media.

(Column 1, lines 27-29.)

2,552,775, P. W. Fisher & J. F. Cook, Drilling Fluid, May 15, 1951,describes a drilling fluid having polyacrylic acid of a molecular weightfrom 5,000 to 50,000 as an alkali metal salt such as the potassium orsodium salt containing sodium carbonate or sodium chloride andbentonite. Example 5 discloses a fluid having 5% bentonitic clay, 7%sodium carbonate and 1% potassium polyacrylate, (about 3.5 pounds perbarrel), all by weight, which is then weighted with barytes to 80 poundsper cubic foot.

2,616,818, Julian L. Azorlosa, Paper Coating, Nov. 4, 1952, discloses aprocess for coating paper using an aqueous dispersion of clay containingabout 50 to 65% total solids and about 6 to 10% polyacrylamide based onthe weight of the clay as an adhesive. Glyoxal is added to render theadhesive substantially insoluble in water. Table I of this patent showsa 100% polyacrylamide and also a 90% acrylamide, 10% acrylic acidcomposition for this purpose. Molecular weights are not given.

2,687,374, Mowry and I-Iedrick, Filtration Method, Aug. 24, 1954,discloses the use of polyelectrolytes including polyacrylamide andpolyacrylic acid to aggregate soil to form a filter.

2,718,497, W. N. Oldham & E. L. Kropa, Drilling Muds, Sept. 20, 1955,discloses 0.2 to 8 pounds per barrel (about 0.057% to about 2.3% byweight) of a polyacrylamide or polyacrylonitrile hydrolyte having amolecular weight from about 10,000 to 2,000,000 and discloses that witha polyacrylamide the hydrolysis may be at least partially accomplishedby sodium carbonate in the well at the temperatures attained in use inthe well. A high solids mud is described having a specific gravity ofabout 1.3.

2,723,956, Carl E. Johnson, Boiler Scale Reduction Using a Copolymer ofMaleic Anhydride and Another Monoethylenic Compound, Nov. 15, 1955,relates to reduction of scale in boilers using copolymers of maleicanhydride and another polymerizable monomeric compound within the rangeof 0.5 to 2,0 grains per gallon of feed water.

2,729,557, Booth and Hedley, (Cyanamid), Method of PreventingDeposition'of Alkaline Earth Metal Salts in Cyanidation of PreciousMetal Ores, Jan. 3, 1956, shows hydrolyzed polyacrylamide'of a molecularweight of at least 10,000 in a cyanidation process.

2,740,522, Aimone and Booth, (Cyanamid), Flotation of Ores UsingAddition Polymers as Depressants, Apr. 3, 1956, relates to molecularweights of about 10,000 and up in a flotation system mentioningcopolymers of acrylamide and acrylic acid among others.

2,745,744, Weidner and Dunlap, Treating Agents Incorporation, May 15,1956, discloses polyelectrolytes in paper making and to cause colloidaldispersed solids to adhere to cellulose and other fibers in a watersuspension.

2,751,367, Yost and Frederick, (Cyanamid), Friable Polyacrylate Powders,June 19, 1956, discloses molecular weights of 88,000 to 530,000 (Col. 2,line 50) and 75% COONa and 25% -CONH mixed With certain insoluble claysand silicates.

2,754,623, Mowry and Hedrick, Erosion-Stable Soil, July 17, 1956,discloses polyacrylamide, polyacrylic acid and certain other polymersadded to soil to prevent erosion and improve growth characteristics.

2,755,557, R. L. Morgan, (Cyanamid), Drilling Muds Containing AcrylicAcid-Acrylamide Copolymer Salts,

ec. 25, 1956, discloses acrylic acid-acrylamide polymer having amolecular weight of 10,000 to as high as 611,000 with the ratio ofcarboxylic acid groups to amide groups between 10:90 and 65:35 withbentonitic clays in drilling muds. The polymer is recommended at a usagefrom 0.1 to 8 pounds per barrel (about 0.028 to about 2.3% by weight). Atypical mud contains 40 pounds per barrel of a calcium-bentonite clay.With these polymers, as additional polymer was added viscosity increasedand then in many instances at higher concentrations, the viscositydropped down.

2,783,200, Crum and Wilkes, Sludge Conditioning and Dispersing Agentsfor Boiler Water Treatment, Feb. 26, 1957, shows the use of certainacrylic polymers including polyacrylic acid in internal boiler watertreatment particularly in conjunction with disodium phosphate.

2,817,128, John A. Wickett, Foundry Sand Compositions and Process ofMaking, Dec. 24, 1957, relates'tO a water soluble polymer having aweight average molecular weight of at least 10,000 and including amongvery many others copolymers of acrylic acid and acrylamide as bindingagents for foundry sand molds.

2,820,777, Suen and Schiller, (Cyanamid), Process for PreparingPolyacrylamide, Jan. 21, 1958, shows a method of simultaneouspolymerization and hydrolysis of acrylamide for a paper additive, acoating material or a sizing material.

2,894,851, Booth, Walker and Allen, (Cyanamid), Method of Forming aProtective Coating on Cyanidation Tailings and the Resulting Product,July 14, 1959, uses polymers of at least 10,000 molecular weight andcopolymers of acrylamide and acrylic acid among many others to form. aprotective layer on cyanidation tailings.

2,903,345, Hedley and Tabachnick, (Cyanamid), Etching of Barium Glass,Sept. 8, 1959, shows hydrolyzed polyacrylonitrile and copolymers ofacrylamide and acrylic acid, among others in the inhibition of theprecipitation of silicofiuoride and mentions a molecular weight of 5,000to limits of water solubility.

2,978,394, Samuel P. Moyer, (Cyanamid), Polyelectrolytes inElectrolysis, Apr. 4, 1961, mentions a acrylamide 10% acrylic acidcopolymer and a molecular weight of 300,000 in the electrodeposition ofmetals from aqueous systems, including filtration of the system.

2,980,609, House and Moore, (Cyanamid), Clarification of IndustrialWater, Apr. 18, 1961, shows a co agulation of industrial waters with ahydrophilic aminoaliphatic linear polymer having free amine groupsdirectly on the polymer chain and mentions molecular weights of at least2,000, I

2,980,610, Ruehrwein, Process for Treating Water, Apr. 18, 1961,discloses a polyacrylamide polymer for treating water which has hardnessimparting compounds therein.

2,981,630, Ben W. Rowland, Clay Products and Fractionation Treatment ofHeterogeneous Aggregates Such as Clay, Apr. 25, 1961, relates to thefractionation of heterogeneous material such as clay by the use of thesodium salt of polyacrylonitrile among many other materials. This patentdiscloses the separation of dilatant from thixotropic clays using thesepolymers and stresses the non-Newtonian characteristics of the clays.

2,995,512, Weidner and Dunlap, Clarification Process, Aug. 8, 1961,relates to clarifying liquid suspensions disclosing a large number ofpolymers, but claims particularly polyelectrolytes with quaternaryammonium nitrogen mentioning particularly polyethylene imine.

3,022,279, Proffitt, Process for Making Hydrolyzed Polyacrylamide, Feb.20, 1962, shows a method for producing a high molecular weight watersoluble hydrolyzed polyacrylamide which is disclosed as desirable in thesedimentation of finely divided suspended solids from aqueous media andin certain other uses.

3,025,236, Barrett and Sauber, Flocculation of Solids, Mar. 13, 1962,shows the sodium salt of sulfonated dodecyl diphenyl oxide and anacrylamide polymer as a flocculating agent.

3,033,675, Norman Hedley, (Cyanamid), Increasing Precious Metal Recoveryin Cyanidation, May 8, 1962, shows copolymers of acrylamide and acrylicacid and others with a molecular weight of 5,000 to 100,000 in a systemin which Zinc dust is added for the recovery of gold and silver.

3,040,820, I. P. Gallus, Method for Drilling With Clear Water, June 26,1962, discloses the use of acrylamide polymer, about 0.8% to hydrolyzed,at levels of 0.001 to 0.02 pound per barrel as it enters the well withclear water as a drilling fluid. The polymer is used as a non-selectiveflocculant in a drilling fluid in which clays are absent. Polymer isalso added to the drilling fluid as the fluid enters the mud pit.

3,040,821, M. B. Widess, Drilling Wells With Clear Water, June 26, 1962,discloses the use of an acrylamide polymer hydrolyte, about 0.8% to 10%hydrolyzed, which polymer is used in slugs to remove cuttings in slugs.The water circulated has less than 0.5% solids.

3,070,543, P. P. Scott, Jr., Low Solids Drilling Fluid, Dec. 25, 1962,discloses a low solids drilling fluid containing from 0.01 to about 0.5pound per barrel of a water-soluble vinyl-maleic copolymer which ispolymerized to a viscosity of between 1 and 3 centipoises for an 0.4%solution in water at 25 C., which drilling fluid contains from 2% t0 7%by weight of montmorillonitic clay. The use of 0.5 to 1.5 pounds perbarrel of sodium carbonate is disclosed. The sodium carbonate enhancesthe action of the polymer. (At least some of the polymers disclosed havea molecular weight of about 250,000 to 500,000.) 2

3,072,569, F. H. Siegele, (Cyanamid), Drilling Fluid Compositions, Ian.8, 1963, discloses a drilling fluid comprising a high calcium contentclay and as a fluid loss control agent a hydrocarbon chain polymercontaining hydroxyl and carboxylic groups in the ratio of 70:90 to30:10. The use of vinyl alcohol-sodium acrylate copolymers areexemplified, particularly for high calcium, high solids, hightemperature drilling.

3,080,264, Zimmie et al., Method of Removing Silt From Tanks, Mar. 5,1963, shows polyelectrolytes with a molecular weight of 100,000 to15,000,000 for removing accumulations of silt and mud from ballasttanks. Here the polymer mechanically aids in causing the mud and siltsto remain in a pumpable form.

3,081,260, A. Park, Low Solids Drilling Fluid, Mar. 12, 1963, disclosesa mixture of montmorillonitic clay and 6 polyacrylamide hydrolytes,about 0.8% to 10% hydrolyzed. The use of sodium carbonate is disclosed.

3,085,916, Zimmie et al., Method of Removing and Preventing Accumulationin Cooling Systems, Apr. 16, 1963, discloses the use of the samepolymers as in 3,080,- 264 for the combined removing and preventing ofaccumulation of mud and silts in water-cooled heat exchangers andcooling systems.

3,102,548, Smith et al., (Cyanamid), Process for Enhancing the Flow ofFluids, Sept. 3, 1963, discloses the use of a polyacrylamide to reducefriction loss under turbulent flow conditions of aqueous fluids.

3,110,666, Hedley and Tabachnick, (Cyanamid), Preventing Deposition ofCopper and Iron Salts From Alkaline Aqueous Solutions, Nov. 12, 1963,shows a polymer of at least about 10,000 molecular weight of acrylamideand for acrylic acid, among many others in the inhibition of iron andcopper compound deposition.

3,118, 832, Katzer and Pye, Control of Silt Load and Scouring in FlowingStreams, Jan. 21, 1964, shows using polyacrylamide and hydrolyzedpolyacrylamide to control the deposition of silt loads in flowingstreams.

3,128,249, Pye and Schura, Method for Clarifying Water, Apr. 7, 1964,shows the combined use of bentonite and acrylamide copolymers inclarifying turbid water.

3,130,167, Jerome Green, Coagulating Composition, Apr. 21, 1964, relatesto the use of a coagulating composition mentioning sodium polyacrylatemixed with bentonite. Column 6, lines 35 to 38 indicates a molecularweight of 10,000 to 100,000 and a ratio of polymer to clay of around 1:1to 1:20. This patent discloses the addition of the clay as part of thecoagulating composition rather than the use of the polymer to removeclay.

3,147,218, Booth and Linke, (Cyanamid), Separating Mineral Fines WithCationic Polyacrylamides, Sept. 1, 1964, shows data on the eifect of pH,concentration etc. on cationic, non-ionic and anionic polyacrylamidesfor separating fines.

3,157,599, W. Gloor, Drilling Fluid, Nov. 17, 1964, discloses a divinylether-maleic anhydride copolymer or poly(acrylic acid) as a water losspreventative with various muds.

3,170,814, Stroia and Voda, Method of Cleaning Sewer Systems, Feb. 23,1965, shows the use of an organic polyelectrolyte such as hydrolyzedpolyacrylamide in causing buoyant materials such as leaves, twigs etc.to float the heavier materials in cleaning sewer systems.

3,171,805, Suen and Schiller, (Cyanamid), Flocculation of Sewage, Mar.'2, 1965, shows the use of synthetic polymers which are cationic incharacteristic with a molecular weight of 10,000 and up in the treatmentof domestic and industrial wastes.

3,215,680, Kolodny, (Cyanamid), Polymeric Compositions and Process forPreparing the Same, Nov. 2, 1965, discloses a method of making highmoleclular weight polymeric compositions which are useful inflocculation.

3,312,070, Matsuo et al., Method of Making Reclaimed Ground WithCoagulative Surface Active Agents, Oct. 11, 1967, shows the use ofpolyacrylamide and other polymers added to the delivery pipe in dredgingoperations to cause the fines and larger particles to drop out morehomogeneously to form a more uniform fill in dredging operations.

3,418,237, Booth and Dobson, (Cyanamid), Settling of Non-Argill'aceousOre Pulps and Mineral Suspensions by Use of Water-Soluble AcrylicPolymers, Dec. 24, 1968, (filed Dec. 22, 1953), shows copolymers ofacrylamide and acrylic acid with a molecular weight of at least 10,000for improving settling filtration and characteristics of ore pulps andmineral suspensions. The references cited, including those added by aCertificate of Correction, not herein specifically listed, are herebyincorporated by references.

3,419,502, Newman, Process for Dispersing Solids in an Aqueous System,Dec. 31, 1968, shows a process for dispersing and maintaining adispersion of various solids that occur in surface Waters. A partiallyhydrolyzed polyacrylonitrile having a molecular weight of not greaterthan 40,000 is shown.

3,425,802, Robert B. Booth, (Cyanamid), Flocculation of Impurities inAlum Solutions, Feb. 4, 1969, relates to acrylamide-acrylic acidcopolymers with an least 60% amide groups and a molecular weight of atleast 10,000 to improve the clarification of hot acidic alum solutionsin alum manufacture.

3,434,970, Siegele et al., (Cyanamid), Selective Flocculant in DrillingMuds, Mar. 25, 1969, shows specific polymers of acrylic acid andacrylamide to increase oil well drilling efficiency, with the drillingfluid being such that drill cuttings separate rapidly but a sodiumbentonitic clay remains in the drilling fluid.

3,463,730, Booth and Mead, (Cyanamid), Prevention of and Removal ofScale Formation in a Water System, Aug. 26, 1969, shows a polyacrylamidein the molecular weight range of 1,000 to 8,000 with about tounhydrolyzed amide groups for scale inhibition.

3,480,761, Kolodny and Booth, (Cyanamid), Clear Overflow Settling WithVery High Molecular Weight Poly- Electrolytes, Nov. 25, 1969, shows avery high molecular weight polyacrylamide with a very low degree ofhydrolysis in the flocculation and polymerization of solids from anaqueous system.

3,488,718, Innes and Paul, (Cyanamid), Filtration of Hydrous Oxides,Jan. 6, 1970, (original filing Aug. 14, 1952), shows using specificpolyelectrolytes for the improvement of the filtering and washingcharacteristics of synthetic hydrous oxides.

3,508,407, Booth, (Cyanamid), Mine Backfill Process, Apr. 28, 1970,shows polyelectrolytes including hydrolyzed polyacrylamide to retaincement fines with coarser particles in mine backfilling operations.

3,516,932, Hedrick and Mowry, Clarification of Water, June 23, 1970,shows the use of homopolymeric acrylamide in clarifying an aqueoussuspension in which the particles are already flocculated by aninorganic salt.

Great Britain, 724,683, Feb. 23, 1955, discloses a boiler water treatingcomposition consisting of a polyacrylic acid as a water-soluble salt anda water softening agent such as the alkali metal carbonates bicarbontes,orthophosphates and polyphosphates. Page 2, lines 50 and following inpart reads: In general, polyacrylic acids of a molecular weight from aslow as 1,000 to as high as 30,000 or 50,000 or even 80,000 may be used.

Canadian 477,265, Azorlosa, Preparation of Paper Products, Sept. 25,1951, shows a copolymer of acrylamide and acrylic acid incorporated in apaper furnish to increase the wet and dry strength of the paper.

Canadian 539,813, R. L. Morgan, (Cyanamid), Nonhygroscopic HydrolyzedPolyacrylonitrile Salts, Apr. 23, 195 7, discloses a dry mixture of ahydrolyzed acrylonitrile polymer having a molecular weight of from75,000 to 300,000 on bentonite as a carrier.

Canadian 589,543, Booth (Cyanamid), Flocculation of AqueousPolyacrylamides, Dec. 22, 1959, discloses the maintaining ofpolyacrylamide in aqueous solution from time of manufacture until use,thus preventing the degradation of polymer characteristics from themechanical aspects of drying and handling.

Canadian 615,987, R. B. Booth (Cyanamid), Fluidizing Aqueous Suspensionsof Solids, Mar. 7, 1961, is the Canadian equivalent of applicants parentcase.

Canadian 642,565, R. L. Morgan (Cyanamid), HydrolyzedChlorate-Polymerized Polyacrylonitriles in Drilling Muds, June 12, 1962,discloses an aqueous clay suspension with 2 lbs. per bbl. of hydrolyzedolyacrylonitrile.

Canadian 662,534, Masselli and Booth (Cyanamid), Chemical Treatment ofOrganic Wastes, May 7, 1963, shows polyelectrolytes in the treatment ofsewage alone and with inorganic electrolytes.

Canadian 700,862, F. M. Aimone (Cyanamid), Poly- Electrolytes inDrilling Operations, Dec. 29, 1964, shows a polyelectrolyte of molecularweight of at least 5,000 to 20,000,000 in drilling with water.

In re Azorlosa, 113 USPQ 156 (CCPA, 1957), rejects claims on copolymerof acrylic acid with acrylamide as a wet strength paper resin.

Prior art cited in parent applications is hereby incorporated by thisreference.

For systems of inert solids in a viscous fluid, Stokes law gives therate of fall. When a small sphere falls under the action of gravitythrough a viscous medium its ultimately acquires a constant velocity,

where a is the radius of the sphere, d and d the densities of the sphereand the medium respectively, and 1 the coefficient of viscosity. V willbe in cm. per sec. if g is cm. per sec. a in cm., d and d in g. per cm.and 1 in dyne-sec. per cm. or poises.

Here, the particles, particularly in the presence of the polyelectrolytehave a layer of bound water, which increases their effective size, andreduces the difference in density. Also, and probably more importantly,Stokes law is only valid where each falling particle is unaffected byadqacent particles. In the present systems, enough particles are presentso that each is affected by its neighbors. This is called hinderedsettling as each particle hinders the movements of its neighbors. Suchsystems often have too many uncontrollable variables for effectiverigorous theoretical treatment, and empirical results are fitted togeneralized equations.

DETAILED DESCRIPTION It has now been found that by introducing fromabout 0.005 to 5 pounds per ton of suspended solids of a polyelectrolyteinto the aqueous suspension there is a tendency for the finer particlesto integrate with larger and give a composition of more uniformcharacteristics, and hence fluidize the suspension.

The fluidization is particularly useful at comparatively high solidconcentrations and in fact makes feasible the use of concentrations ofsolids which were previously regarded as completely inoperable. Inorther words by using the present novel fluidizing agents, a higherpercentage of solids can be handled in leaching, stirring and agitatingoperations and the suspensions can be treated in tanks and otherequipment and more uniformly and smoothly fed through pipes, valves,bends, turns, sumps, siphons, pipelines, etc. than has been previouslypossible with known fluidizing agents. The high degree of mobility thusimparted to the ore suspensions definitely facilitates their handling.

The effect which herein is called fluidizing, or anticaking oranti-packing, is rather difficult to explain theoretically. In certaintests, for instance, it is found that if a suspension of a mixture offine and coarse minerals is agitated, the material remains fluid andfairly easy to handle. If, however, stirring is stopped, the coarsersolids rapidly drop out and thus form a stable dense layer. Incontradistinction therto by using the present polyelectrolytes there isformed a fluidized suspension in which the solids drop uniformly, if atall, as a homogeneous fluidized mass so that on moderate agitation thesolids are again uniformly suspended.

The use of the polyelectrolyte fluidizing agents is highly beneficialand gives improved results in the leaching of a variety of ores,concentrates, roasted and calcined products, metallurgical slags andmattes and residues, which contain uranium, cobalt, and other raremetals, copper, nickel, zinc, manganese, calcium phosphate, titanium,alumina, bauxite, bauxite clays, kaolins, etc. Such leaching may beconducted at atmospheric pressure in vessels equipped With air and/ orin mechanical agitators, or in Pachuca-type tanks equipped with airlifts for circulating the ore pulp, and also under pressure in speciallyconstructed tank or autoclaves. In such leaching operations temperaturesrange from room temperature up to 100 C., or higher if pressure vesselsare used. Various acids such as sulfuric, sulfurous, nitric, phosphoric,and hydrochloric acids are used in such leaching operations. Also acidsmay be autogenously generated by simply adding water to dissolve theacid constituents of ores or concentrates and the resulting acidicliquors used for leaching purposes.

The effect of the polyelectrolytes is particularly useful in operations,such as the extraction of uranium from uranium ores, in Which the ore isleached with an acid, such as sulfuric acid or nitric acid. As theleaching occurs, it is preferred that the system be such that moderateagitation can be employed, rather than high speed violent agitation, toprevent the dropping out of a layer of ore solids. Also, it is highlydesirable that the suspension be such that should a power failure occur,the settled solids in the leach tank do not set up so as to requirelaborious and time-consuming manual clean-outs.

'In the processing of ores, and particularly uranium ores, the markedadvantages introduced by the present fluidizing may be utilized in anyof several ways. The present fluidizing agents allow leaching to beconducted over a wider range of pulp densities than previously used. Itis possible to use smaller agitation equipment to keep the solidssuspended, or to use less power for agitation; or in the case of someores, to use a higher solids concentration in the pulp so that more orecan be processed through a given series of leaching vessels; or to usethe improved fluidization to permit the utilization of less finelyground ores and save in the cost of grinding of the ore. The advantagesof the present fluidization may be utilized in part by taking advantageof any or all of these process improvements. The leached solids canconveniently be manipulated with a size range of an ap preciablefraction, of up to 50%, larger than 65 mesh, or With up to 50% smallerthan 325 mesh, or any intermediate ratios.

In addition to the increased flexibility of operations, there is atremendously important advantage that should any portion of a fluidizedsystem remain unagitated even for considerable periods, the solidsremain in a fluidized state so that immediately on resumption ofagitation or circulation the materials flow readily.

The polyelectrolyte may be added at any point in processing where it isdesired to prevent the heavier particles from settling out, and tomaintain a fluidized state. The polyelectrolyte may be used inconjunction with agents, such as glue or gelatin, or may be used alone.All of the fluidizing agent may be added initially, or part of thepolyelectrolyte may be added initially and additional quantities addedafter part of the leaching has taken place.

Such staged additions as above are preferred by many operatorsparticularly if the ore suspension is processed for long periods oftime. Additional quantities of the same or different polyelectrolyte maybe added to assist in a subsequent dewatering operation in which thefluidized solids are separated from the aqueous phase by filtration ordecantation, such as land fill of tailings, or from dredging operations.

The polyelectrolyte fluidizing agent may be added as a solution or indry sub-divided solid form to the suspended solids. Dry additions arepreferred in many operations, especially those of long duration whereinthe suspension is processed over several hours or several days. In suchcases, the feeding of staged additions of the polyelectrolyte as a drysolid is the preferred practice. For example, in continuous leaching ofores in agitators arranged in series, excellent results are obtained byfeeding continuously small amounts of the polyelectrolytes in dry solidform to some or all of the agitators in the series. Continuous feedingto batch leaching also gives excellent results. The preferredpolyelectrolyte fluidizing agents dissolve so as to be present inconcentrations suflicient to impart the desired improved fluidity to thesuspension of mineral solids. The polyelectrolyte may also be added as asolution in water or other solvent and as such may be fed in a singlestage, in multiple stages or continuously. Solutions of thepolyelectrolyte are particularly convenient for small scale operations.Solid feed is more convenient for larger operations.

The polyelectrolytes may be added to the suspensions of solids in waterin various fashions. For example, the polymers may be added to thesolids before the solids are suspended, or they may be added to thewater or solutions in which the materials are to be suspended or may beadded to the suspension after it is formed. For convenience in measuringsmall amount of the added polyelectrolyte, it is particularly convenientto dissolve the polyelectrolyte in water to form stock solutions of 1-5concentration, which may be diluted if desired to allow accurate feedingof small quantities.

In feeding dry polyelectrolytes, a vibrating type feeder, or other typefeeder may be used to slowly feed the system. A slow flow of solidparticles is easily dispersed, and lumping of the polyelectrolyte doesnot occur. The usual equipment used for feeding liquid reagents inmineral dressing practice may be used for feeding solutions of thepolyelectrolytes.

All or a major portion of the polyelectrolyte may be added initially,but, the polyelectrolyte appears to be absorbed on the surface of finesin the mineral suspensions and better results are obtained with a givenamount of polyelectrolyte, or the same results with a smaller amount ofthe polyelectrolyte, if the addition is gradual during the period ofagitation in leaching, or other treating of the ore.

Additional quantities of the polyelectrolyte may be added after theleaching is complete to act as a flocculant in separating the ore fromthe water or aqueous solutions in the suspension.

The polymers which are found to be effective in the fluidizing ofaqueous suspensions of solids are Water soluble polymers of a compoundrepresented by the formula:

wherein R is selected from the group consisting of nitrile, amide, andcarboxyl radicals, COOM where M is a lower alkyl radical preferably of 1to 4 carbon atoms, and the Water soluble salts thereof. Elements such ashalogens, particularly chlorine, or alkyl or aryl groups as well ashydrogen may be present on the backbone hydrocarbon chain of thepolymer.

Suitable polymers for use in the present invention may be obtained bypolymerizing acrylic compounds, such as acrylic acid or derivativeshaving groups which are hydrolyzable to acid, such as, for example,acrylonitrile, esters of acrylic acid, etc. Chloroacrylamide ormethylacrylamide give polymers with substituents on the backbone.Acrylic acid or acrylamide may be polymerized to form homopolymers ormay be copolymerized with other compounds of the group or small amountsof other compounds, such as diallyl dimethyl ammonium chloride, vinylpyridine, vinyl acetate, styrene, vinyl ethers, vinyl halides, orunsaturated hydrocarbons such as isobutylene. Particularly useful arepolyacrylic acid, polyacrylamide, hydrolyzed polyacrylonitrile,including acid-hydrolyzed polyacrylonitrile, and alkali-hydrolyzedpolyacrylamide, and acrylic acid-acrylamide copolymers. Water-solublecross-linked polyacryl'amides are also useful and methylenebisacrylamidein small quantities is a highly useful cross linking agent. Thesepolymers of low, medium, and high viscosities, or molecular weight rangeare satisfactory. Molecular weights as low as 100,000 are useful.Molecular weights of Well over 3 million are preferred. A long as thepolymers are sutficiently low in molecular weight to be water soluble,they have the characteristics required. Polymers of molecular weights ofat least 20 million have such attributes.

The upper limit is very ambiguous as different methods of measuringmolecular weight give materially different values, since differentmeasurements by supposedly reliable methods give variations of 2,000,000to 5,000,000 in the molecular weight of a single polymer. Viscositymeasurements, particularly intrinsic viscosity determinations, are aconvenient method of characterizing polymers, as described by M. L.Huggin in Industrial and Engineering Chemistry, Volume 35, pages 980986(1943). Viscosity determinations may be conducted by well known methodssuch as by an Ostwald viscosimeter at polymer concentrations of ODS-0.5%at 30 C.

Polyacrylamide, polyacrylic acid and hydrolyzed polyacrylonitrile havethe general formula:

where n, m and o are whole numbers, and the groups within theparentheses occur in random order and orientation. It is at least 3, andmay be zero, and m may be zero,

but preferably m is greater than n. The groups can be referred to ascarboxyethylene, carbamylethylene and nitriloethylene, respectively. Thecarboxy group, of coure, can exist as its salt, and as an alkali saltsuch as sodium or in solution in ionized form, and such forms are thenatural and inherent equivalent of the carboxy form itself in thepresent suspension system, as enough cations of various salts arepresent in the solids and water to react with free carboxyl groups, toform salts. The free acid with polyacrylamide, or the sodium salt ofhydrolyzed polyacrylonitrile are frequently preferred commercially.

The nitriloethylene group is not inherently required and is normallyonly present in small proportions representing an unhydrolyzed fractionfrom the polymerization of materials containing acrylonitrile. At leastsome carboxyethylene linkages are present in all commercial products. Inpolymerization of acrylamide, at least a small fraction is hydrolyzed,and at least three carboxy groups are present per molecule, even thoughwith molecular weight of over a million, the actual percentage can bevery small.

By historical custom, many of the present polyelectrolytes are referredto and named as polymers of the more conventional starting materials,such as polyacrylamide or polyacrylic acid, although the same compoundcan be formed by the hydrolysis of polyacrylonitrile, hydrolysis ofpolyacrylamide or copolymerization of acrylamideacrylic acid. Thus, ahydrolyzed polyacrylonitrile is actually essentially apolycarbamylethylene-polycarboxyethylene polyelectrolyte.

A minor proportion of linkages from the other vinyl compounds abovereferred to may be present, to adjust the cationicity, anionicity, orcharge along the polymer chain, and where not highly branched orcross-1inked the polymer remains soluble. Such minor proportions may bedesigned in to change the charge, or may result from impurities duringmanufacture. Salts produced during manufacture may remain with thepolymer, as may solubilizing materials. A small amount of sodium sulfateor a lower alkanol can improve the solubility of the high molecularweight polymers.

The polyacrylamides are particularly effective in acid leaching, such asused with uranium ores. The polyacrylamides retain their efii'ciencyeven at a pH more acid than 1. Polyacrylic acid and hydrolyzedpolyacrylonitriles are also particularly useful for alkaline circuitscontaining alkaline earth minerals.

The present effect is particularly useful where there is a wide range ofparticle size present. For instance, while a polyelectrolyte is usefulas a fluidizing agent if added to a suspension of uniformly sized coarsematerials, it is much more effective if fines are also present.

The exact size range over which the present effect occurs is very wideindeed. It is particularly useful when some of the suspended materialsare comparatively c0arsethat is, are retained on a 65 mesh per inchscreen and others are comparatively fine, that is, readily pass a 325mesh to the inch screen.

More coarsely ground ores may be leached in the presence of the presentfiuidizing polyelectrolyte, as such coarse material does not then clogup the agitators. The use of the fluidizing polyelectrolyte permitsconcurrent treatment of the sands and slimes instead of using separateleaching circuits, as it permits the leaching of a more coarsely groundore under a particular set of conditions. With ores or minerals in whichthe specific gravity is higher, a finer state of division is normallyrequired for a full fluidizing effect. It is to be noted that even ifcomplete fluidization does not occur, none the less a partialfluidization is extremely useful in maintaining circulation.

The theory of interaction is not well developed. Probably the polymerattaches to the surface of both coarse and fines, and binds water sothat the particles have a layer of bound water, which adds to theapparent size, and reduces the apparent density difference, so thatStokes law requires major correction factors to apply, and at least partof the polymer chains bridge between particles. This causes the finesand coarse to act as a more homogeneous material, with water being ineffect filtered out, instead of a settling of particles in water, and asa result, the settled solids are readily resuspendable, or even if longsettled, are more easily suspended. This applies to resuspendingdeposits in leach tanks, storage tanks, cooling or heating tanks,treating vessels, pipelines, and other places where the coarse solidscould settle out and inhibit flow, and be difiicult to resuspend; orhave settled out, and when resuspended tend to rapidly resettle. Anothereffect is that the polymer increases the viscosity of the aqueous phase,and as thicker, keeps the particles more readily resuspendable. The useof these polymers increases pipeline capacity in turbulent flow, see3,102,548, supra, and the greater scour induces improved suspension andresuspension characteristics in the systems.

This application is not predicated upon the correctness of any theory ofoperation, but such a theory of operation does make the illogical seemmore comprehensible, even if it still remains unobvious. But thesecharacteristics permit tremendous advantages in settling of solids toprovide a more homogeneous material, whether as a resuspendable solid ina leach tank, a land fill for dredging, silts in heat exchangers, orballast tanks, or sewage solids in a disposal plant.

The efficacy of fluidization is more easily illustrated with a mixtureof just coarse and finesin most operating embodiments, the range ofparticles sizes would be a continu- 'ous spectral.

Certain of the examples show just coarse and fine for purposes ofillustration. The continuous range shown in samples from commercialgrinding operations is more typical of normal usage. A rapidlyclassifying fraction of +65 mesh materialover about 5% of the totalsolidscauses the problem in commercial operations. The density ofcomponents and degree of agitation enter. The greater the particledensity, and the lower the agitation, the less suspending action fromliquid turbulence, and the greater the need for polymer suspendingaction. When flow suspending action ceases, as during power outages, thetime and character of suspended particles is a factor in ease ofresuspendability. The economic factors can readily control the amount ofpolymer added, as a small amount may be .sufiicient to give neededresuspendability. Often if the polymer is added when resuspending isdesired, adequate re- 13 sults are obtained. Often, the use of thepolymer permits a coarser grind in milling operations, With an adequatesafety factor of resuspendability. This is particularly controlling inoperations where resuspendability had been the controlling factor infineness of grind.

-.FIG. 1 shows the suspending effect of polyacrylamide versus glue as afunction of concentration.

2 showsthe suspending effect of polyacrylamide versus glue as a functionof pH.

, Whereas the exact scope of the present invention is set out in theappended claims, the following specific examples illustrate certainaspects of the present invention, and more particularly point outmethods of evaluation or testing to show the unique advantages offiuidization with polyelectrolytes. All parts are by weight, unlessclearly otherwise set forth.

EXAMPLE 1 A uniform suspension of ground silica in water, about 620 ml.in volume and 60% solids (weight/weight) in pulp density, is prepared bythe addition of 300 grams of plus 150 mesh silica and 300 grams of minus200 mesh slicia to 400 grams water which contains sufiicient sulfuricacid to give arpH of 1.0 to the final suspension. The plus (150 meshfraction contains about 48% of plus 65 meshmaterial and about 3% plus 48mesh material. The mixture is agitated with a plunger for about 30seconds, thus forming a uniform suspension. The suspension is allowed tostand for two minutes during which time the coarse fractions of thesuspended silica are observed to drop out rapidly. Then the upper halfof the suspension, is drawn off and filtered. The filter cake is driedand screen analyzed to determine the content of plus 150 mesh silica.

A series of tests as above were run in which the silica suspensions wereallowed to stand for the two-minute period after treatment with variousamounts of a polyacrylamide with a molecular weight of approximately 2million. A second series of tests were run under the same conditionsusing glue instead of polyacrylamide. The glue or polyacrylamide weredissolved in 100 gram portions of the water used to suspend the silica.

The amounts of plus 150 mesh silica contained in the upper half of thesuspension at the end of two-minutes settling period at a pH of 1.0 werefound to be as follows:

f These results are graphically presented in FIG. 1,

which clearly demonstrates the superiority of polyacrylamide to glue asa fluidizing agent.

EXAMPLE 2 Uniform suspensions of mixed +150 and 200 mesh silica areprepared as set forth in Example 1 and treated ''with polyacrylamide andglue at the natural pH of the suspensions, pH 5.6. The amounts of +150mesh silica in the upper half of the suspension after the two-mmute 14settling period in one particular run at a pH of 5.6 was found to be asfollows:

Uniform suspensions of mixed and 200 mesh silica are prepared asdescribed in Example 1. The natural pH of such suspensions is 5.6. To aseries of such suspensions sulfuric acid or sodium hydroxide is added soas to vary the pH over the range of 1.2 to 8.5. To each suspension 0.01pounds per ton of polyacrylamide is added. To a second series ofsuspensions with a similar pH range, 0.13 pounds per ton of glue isadded. Following the addition of polyacrylamide or glue in solution asdescribed in Example 1, each suspension is agitated and then allowed tostand for two minutes. The upper half of the suspension is drawn off andfiltered, and the filter cake dried and screen analyzed to determine thecontent of +150-mesh silica.

For one particular typical run the amounts of +150- mesh silicacontained in the upper half of the suspension were as set forth in thefollowing table.

The above data is shown in FIG. 2. The particularly wide range of pHvalues over which the polyacrylamide is effective is clearly shown bythis example.

EXAMPLE 4 A sample of Canadian uranium ore is ground to about 48 meshwith 59% 200' mesh in particle size, and leached at 60% solids with 60grams per liter of sulfuric acid is aqueous solution. Samples of theleached pulp containing 600 grams of ore are treated with polyacrylamidein a series of tests and allowed to stand for fifteen minutes afterwhich time the upper 300 cc. of the suspension is siphoned off andfiltered. The filter cake is dried and screen analyzed to determine thecontent of +200 mesh ore solids. A second series of samples of theleached pulp are treated simultaneously with glue, and screen analyzedas above. The polyacrylamide and glue are added in aqueous solution.

The results of one series of tests are shown in the following table.

Pounds per ton of polyacrylamide 1 5 EXAMPLE 5 Samples of 1200 grams ofthe uranium ore described in Example 4 were leached with 60 gramssulfuric acid per liter at a pulp density of 60% solids in 1500 cc.beakers for 6 hours at 45 C. During this time the pulp was agitated withan electrically-driven, cruciform impeller operating at 250 r.p.m.

At the end of this 6-hour period the stirrer was removed and immediatelyin the pulp on the bottom of the beaker was placed a flat, stainlesssteel circular disc, inch thick and 1.5 inches in diameter, to which atthe center a stainless steel rod, 4 inch in diameter and 8 inches inlength was atached. This rod was equipped with a hook at its upper endso that it could be attached to a 2000 gram spring balance and thus thepull required to start the disc upward through the pulp could bemeasured. The pull is measured after the pulp is permitted to stand fora specified period of time. This testing method is similar to methodswhich have found acceptance in the industry to distinguish pulps whichcause trouble and is highly useful in determining the degree ofcompaction that ore or mineral suspensions exhibit on standing.

A series of tests were run by this procedure in which the agitation timewas varied from 6-24 hours and the standing time from 16-54 hours.Polyacrylamide or glue in dry solid sub-divided form were added at thestart of these tests and the results obtained were compared with thoseof control tests on leached ore pulp without such fluidizing additives.The results of these tests are sumand an additional 0.12 lb. per ton ofore, fed continuously in equal portions divided among the 'sixagitators. Thus, the total requirements were 6,360 pounds, which amountsto one-tenth of the quantity of glue used in similar operations in thefirst series of agitators. The fiuidization with polyacrylamide was moreelfective than with the glue. A convenient test as used in'the industryis to take a liter of the ore suspension, three times a shift, in agraduated cylinder, allow to stand for five minutes, and measure thesands dropping out into the botton of the graduate. In the above testwith polyacrylamide 10 cc. of such sands were noted as compared with 40to 60 cc. with glue. This shows the polyacrylamide to be more effectivefor fiuidizing purposes than 10 times as much glue.

EXAMPLE 7 A 100,000-ton lot of uranium ore was leached as described inExample 6. In the first series of agitators 6360 lb. of polyacrylamideof about 2 million molecular weight was added as a fluidizing agent,which was used as also described in Example 6. No clogging or stoppages.of agitators during the course of the leaching operations were noted.

In the second series of agitators no fiuidizing agent was added. In thiscase agitator stoppage occurred in some of the leaching tanks beforethese tanks were completely filled, because of drop-out of coarse solidsat the bottom of the tanks. In other tanks the agitators operatedfor afew hours and then stalled for the same reason. 'Le'aching marized inthe following table. 30 operations had to be suspended in this sectionof the Hours 01- Run Material added Agitation Standing Balance reading,grams 1 None 6 16 1,600.

0.1 lbs/ton polyacrylamide- 6 16 800. 3. 0.1lbs./ton polyacrylamidc 6 541,000. 4 0.7 lbs/ton glue 6 16 1,200. 5 None 24 24 Balance pulled ofiscale and lifted beaker and contents 011 table. 6 0.1lbs./tonpolyacrylamide- 24 24 1,200. 7 0.7 lbs/ton glue 24 24 Balance pulled olIscale.

The above tests simulate conditions which occur in the processing of orepulps in various operations during plant shutdowns, power-outs, etc. andthe above results clearly demonstrate the effectiveness of small amountsof polyacrylamide in overcoming the compacting of ore suspensions onlong periods of standing.

EXAMPLE 6 A 100,000-ton lot of uranium ore was processed continuously atthe rate of 3000 tons per day as follows: the ore was ground to minimum48 mesh and leached to extract uranium at 65-68% solids in water with 60grams sulfuric acid per liter in the presence of 4.0 lb./ ton sodiumchlorate. Leaching temperature was C. The ore fed to the leachingoperation was split so as to pass continuously into two series of sixsimilar size and type tanks equipped with agitators so that each seriestreated 1500 tons per 24 hours. The capacity of the tanks in each serieswas such that the total leaching cycle was 48 hours. Each tank held 250tons of ore and a total of 3000 tons was agitated :at one time. Glue wasused as a fluidizing agent in one series of six agitators andpolyacrylamide was used in the other.

Glue was added in dry granular solid form and glue requirements were 600lb. to each agitator during startup operations and an additional 1.2 lb.per ton of ore was fed continuously in equal portions divided among thesix agitators. The total glue used for effective fiuidization intreating the ore in the first series of agitators was 63,600 pounds.

Polyacrylamide of an intrinsic viscosity of about 5.6 was added in dry,solid flake form. Polyacrylamide used was only 60 lb. per agitatorduring start-up operations plant and the acidic solutions andhard-packed ore were removed by flushing with water and manual digging.

EXAMPLE 8 Percent of total +200- mesh in Intrinsic upper Polymerusedviscosity hal Polyacrylamide 6. 4 43. 7 Do. 5. 5 43. 0 Do. 3.1 43. 5Do. 2. 5 41. 0 D0. 1.8 40.0 90:10 copolymer of aerylonittile-aerylamide.5. 4 41. 0 89:11 copolymcr of 'acrylarnide (AM) diallyldimethyl ammoniumchloride (DADM) 5. 7 42.0 :20 copolymer of Alli-D ADM 5. 4 41.0 96:4copolymer of AMDADM 5.0 41.0 96:4 eopolymer of AMDADM.. 3. 4 40.0 9624copolymer of AM-DADM 1.8 39.0 96:4 copolymer of AM-DADM 1. 4 39. 0 Across-linked polyacrylamide 0 methylenebisaerylamide) l 35. 0Polyacrylamide with 6.2% of the amide groups hydrolyzed to carboxylgroups 5. 7 29. 0

1 Molecular Weight about 2 million.

EXAMPLE' 9 A nickel-cobalt ore, assaying 1.2% Ni and 0.14% Co was groundto 50% minus 200 mesh and pressure leached 17 for 2 hours with 22%sulfuric acid at 30% solids. 91.2% of the nickel and 92.0% of the cobaltwas extracted in the leaching operation.

Treatment with 0.2 lb./ton of polyacrylamide during the leachingoperations allowed the use of a pulp density of 40% solids with otherconditions similar to those listed above. The higher pulp density inleaching did not interfere with extraction as 91.3% of the nickel and92.1% of the cobalt were extracted in this test.

EXAMPLE 10 A manganese ore, assaying about 18.3% Mn, was ground to minus200 mesh and leached at 20% solids with a 6% water solution of sulfurdioxide for 6 hours at room temperature. The residual ore solids werefiltered off, dried, weighed, and assayed for manganese along with theleach liquors. In this operation 87.6% of the total manganese wasextracted.

The above procedure was repeated on a second lot of the same manganeseore to which was added 0.15 lb./ ton of a 90: 1'0 copolymer ofacrylamide-acrylic acid of molecular weight of about 2,000,000 asmeasured by viscosity methods. In this leach a higher pulp density, 35%solids, was employed. No difficulties in agitation during leaching werenoted and an extraction of manganese of 87.7% was obtained, whichduplicated the results of the first leach described above in thisexample.

EXAMPLE 1 l A uniform aqueous suspension of fine silica (-200 mesh) witha total volume of 1,000 millimeters in a graduated cylinder is prepared.This suspension is allowed to stand for three days. During this time,the silica settles to a compacted mass which cannot be poured with thesupernatant liquid by inclining the graduate and must be flushed out bya stream of high pressure water from a laboratory hose in order to cleanout the graduate. The experiment is repeated exactly except that theequivalent of 0.013 pounds per ton of a polycarbamylethylene of 3-5million molecular weight and containing about 1% carboxyethylenelinkages is added to the suspension, by agitation with a perforatedplunger. After standing three days, the major portions of the solids atthe bottom of the graduate were poured out readily along with the water.A similar experiment is run using a long chain polycarbamylethylene ofabout the same molecular weight range containing 5% carboxyethylenelinkages. Again, after three days of standing, the settled solids arepourable along with the supernatant water.

EXAMPLE 12 The experiment described in Example 11 was repeated with asuspension of 150 grams of 150 mesh limestone in one liter of water.After standing for a three-day period, the settled solids remainedcompacted in the bottom of the graduate while the supernatant water waspoured off.

This experiment was repeated using the equivalent of 0.2 pounds per tonof a hydrolyzed polyacrylonitrile as the sodium salt. The settled massat the bottom of the graduate remained fluid after the three-daystanding period and was readily poured from the tube with thesupernatant water.

EXAMPLE 13 A silt-containing river water used for industrial coolingpurposes was treated with 1 part per million of a polyelectrolyte ofmolecular weight 3-5 million which contained 99% carbamylethylenelinkages and 1% carboxyethylene linkages. The treated water was passedinto a settling tank and the suspended solids were settled out. Theclarified water was used for cooling purposes. After a two-week period,the tank was cleaned out by removing the clear supernatant water andflushing out the settled matter by means of a stream of high pressuredwater. Treatment with the polyelectrolyte rendered the settled 18 solidssoft and mobile and prevented the accumulation of compacted masses onthe bottom of the tank. The treatment reduced clean-out time and laborby a factor of about 65%.

EXAMPLE 14 To determine the beneficial efiect of polymer treatment inthe pumping of fine ore materials, a 1% suspension of phosphate rockslimes was treated with 2 pounds per ton of the polyacrylamide used inExample 13.-The suspension was then thickened by gravity to about 16%solids. The solids were thus rendered mobile and amenable to pumping.Compared to a similar sample of untreated slimes, power losses due tofriction were reduced by 25% by the treatment of polyacrylamide, and ifpumping is interrupted, the low points in the pipe system remain freefrom clogging.

EXAMPLE 15 The polyacrylamide used in Example 13 was added in quantitiesin about 10 parts per million to the circulating water in an automobileradiator. The motor of the automobile was operated for a period of 10minutes in order to thoroughly distribute the polyacrylamide throughoutthe entire volume of water in the radiator. The radiator was thendrained by gravity. The suspended sludge and rust solids were kept fluidand mobile and were readily drained out of the radiator by merelyopening the drainage vent at the bottom of the radiator. This result wasin marked contrast with the usual radiator cleaning procedure whichrequired several flushings with water to remove incompletely theaccumulation of rust and sludge.

I claim:

1. A fluidized resuspendable mineral suspension pulp containing solidslarger than 65 mesh and fines smaller than 325 mesh and substantiallyhomogeneous throughout in which the fines are integrated with the coarsematerial by from 0.005 to 5 pounds per ton of solids of a water solublepolyelectrolyte, which is an ampholytic linear carbon chain vinylpolymer consisting essentially of recurring carbamylethylene andcarboxyethylene linkages and not more than a minor amount ofnitriloethylene linkages and salts thereof, having a weight averagemolecular weight in excess of 100,000, thereby producing a suspensionwhich is of uniform characteristics, from which the solids drop out asan unclassified readily resuspendable thixotropic material, said polymerincreasing the viscosity of the aqueous phase, insuring laminar flow athigher velocities, thereby reducing pumping power requirements, andsimultaneously stabilizing the suspension, so that during interruptionsin agitation, the suspension remains fluidized, and in pumpablecondition.

2. The suspension of Claim 1 in which the polyelectrolyte has a majorproportion of and which suspension, at least when allowed to settle, hasa high solids content of at least about 30% solids by weight.

3. The suspension of Claim 2 in which the polyelectrolyte has thestructure, in acid form:

H our-on oH, oH om-o -11 41:0 =0 111111 In 1 o it n where n, m and 0 arewhole numbers, and the groups within the parentheses may occur in randomorder and orientation.

19 4. The suspension of Claim 1 in which the polyelectrolyte is i 7 'H-orb-on -11 References Cited UNITED STATES PATENTS 3,418,237 12/1968Booth et a1 210-54 3,035,867 5/1962 Corbett 302-66 X Atwood et a1 210-54X Aimone 210-54 X Booth et a1 210-54 Booth 302-66 Innes et al. 210-54Goren 210-54 X Wasp et a1 302-66 BENJAMIN R. PADGETT, Primary ExaminerR. L. TATE, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 42,01Dated October 15, 1974 Intentofls) RQBERT BEN BOOTH It is certified thaterror appears in the shove-identified patent and that said'LettersPatent are hereby corrected as shown below:

001. 8, line 12, delete "its" and insert therefor it Col. 8, line 28,delete "adqacent and substitute therefor adjacent 'Col". 8, line 4'7;delete "orther' and substitute therefor other r Col. 15, in the. tableunder libceznple 1, test 7j, change percent of total from 0.0" to 9.0

- Signed and sealed this 17th dsy of December 1974.

(SEAL) Attest:

trace: 2 1. 'rr c. :aRsmLL mm? Attesting; Officer- 1 v Commissioner ofPatents FORM PO-105D (10-69) USCOMM-DC 60376-P69 w u.s. sovnuuznrPRINTING OFFICE: 19" o-ass-su UNITED. STATES PATENT OFFICE CERTIFICATEOF CORRECTION- Patent No; 3,842,013 Dated October 15, 197

Intentofls) ROBERT BEN BOOTH It is certified that error appears in theabove-identified patent and that said'Letters Patent are herebycorrected as shown below:

001. 8, line 12, delete "its" and insert therefor it Col. 8, line 28,delete "adqacent" and substitute therefor adjacent Col. 8, line 475delete "orther" and substitute therefor other Col. 1 in the table underrxe le' ;1 test 7;, change percent of total from "0.0" to 9.0

- Signed and sealed this 17th dey of December 1974.

(SEAL) Attest:

f-cCOY 3%. (51733 N R. t C. HARSZLXLL DANN attesting; C'fficerCommissioner of Patents F ORM PO-105O (10-69) USCOMM-DC 60376-P69 w u.s.GOVIINIENT PRINTING omcz: nu o-au-su

1. A FLUIDIZED RESUSPENDABLE MINERAL SUSPENSION PULP CONTAINING SOLIDSLARGER THAN 65 MESH AND FINES SMALLER THAN 325 MESH AND SUBSTANTIALLYHOMOGENEOUS THROUGHOUT IN WHICH THE FINES ARE INTEGRATED WITH THE COARSEMATERIAL BY FROM 0.005 TO 5 POUNDS PER TON OF SOLIDS OF A WATER SOLUBLEPOLYELECTROLYTE, WHICH IS AN AMPHOLYTIC LINEAR CARBON CHAIN VINYLPOLYMER CONSISTING ESSENTIALLY OF RECURRING CARBAMYLETHYLENE ANDCARBOXYETHYLENE LINKAGES AND NOT MORE THAN A MINOR AMOUNT OFNITRILOETHYLENE LINKAGES AND SALTS THEREOF, HAVING A WEIGHT AVERAGEMOLECULAR WEIGHT IN EXCESS OF 100,000, THEREBY PRODUCING A SUSPENSIONWHICH IS OF UNIFORM CHARACTERISTICS, FROM WHICH THE SOLIDS DROP OUT ASAN UNCLASSIFIED RAIDALLY RESUSPENDABLE THIXTROPIC MATERIAL, SAID POLYMERINCREASING THE VISCOSITY OF THE AQUEOUS PHASE, INSURING LAMINAR FLOW ATHIGHER VELOCITIES, THEREBY REDUCING PUMPING POWER REQUIREMENTS, SO THATDURING INTER TANEOUSLY STABILIZING THE SUSPENSION, SO THAT DURINGINTERRUPTIONS IN AGITATION, THE SUSPENSION REMAINS FLUIDIZED, AND INPUMPABLE CONDITION.